Shell, Exxon Came Late to the Party, Then Made Massive Investments

Some of the world's biggest energy companies are struggling to make money from massive bets on the shale boom in North America, where deposits of oil and gas are proving abundant but not always profitable.

Royal Dutch Shell PLC, which has had a tough time coaxing crude oil from dense rock formations, said Thursday its shale holdings in the U.S. are worth $2.07 billion less than it had previously determined. The write-down helped...